1. Field of the Invention
The present invention relates in general to acoustic transducer arrays and also relates to a transducer array capable of radiating steered modal based directional acoustic energy.
2. Background and Discussion
Traditionally arrays of sonar transducer are used to form directional beams that can be electronically steered to various directions. They often take the form of planar, spherical, or cylindrical arrays. U.S. Pat. No. 3,290,646, entitled “Sonar Transducer,” by S. L. Ehrlich and P. D. Frelich describes a sonar transducer where beams are formed and steered from a single transducer in the form of a cylinder. Cardioid beam patterns are formed through the combination of extensional monopole and dipole modes of vibration of a piezoelectric tube, cylinder or ring. In the published paper, “Superdirective spherical radiator,” J. Acoust. Soc. Am., 61, 1427-1431 (1977) by J. L. Butler and S. L. Ehrlich, a multimodal spherical shell and array is presented as examples of radiators which can achieve super-directivity through a specified addition of spherical radiation modes. In U.S. Pat. No. 6,734,604, entitled “Multimode Synthesized Beam Transduction Apparatus,” issued on May 11, 2004, there is described a method for directional beam formation using monopole, dipole and quadrupole mechanical modes of vibration of a continuous piezoelectric tube operating as a unitary transducer with steered beam capabilities.
It is a general object of the present invention to provide a transduction apparatus, which employs an array of individual transducers that generates multiple acoustic radiation modes in the medium which yield a directional steered beam pattern.
Another object of the present invention is to provide an array of transduction elements, which generates multiple radiation modes including the quadrupole mode to obtain an improved, more directional, steered beam pattern.
A further object of the invention is to provide an electromechanical transduction array apparatus having beam patterns with desirable beam width, side lobe and null structural properties as a result of the addition of the quadrupole mode.
Still another object of the present patent is to provide an electromechanical transduction array apparatus characterized by a constant beam pattern and smooth response over a broadband operating range from an array of transducers.